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Non-linear magnetic buoyancy instability and turbulent dynamo

Lookup NU author(s): Yasin Qazi, Professor Anvar ShukurovORCiD, Dr Devika Tharakkal, Dr Fred Gent



This work is licensed under a Creative Commons Attribution 4.0 International License (CC BY 4.0).


© 2023 The Author(s). Published by Oxford University Press on behalf of Royal Astronomical Society. Stratified discs with strong horizontal magnetic fields, are susceptible to magnetic buoyancy instability (MBI). Modifying the magnetic field and gas distributions, this can play an important role in galactic evolution. The MBI and the Parker instability, in which MBI is exacerbated by cosmic rays, are often studied using an imposed magnetic field. However, in galaxies and accretion discs, the magnetic field is continuously replenished by a large-scale dynamo action. Using non-ideal MHD equations, we model a section of the galactic disc (we neglect rotation and cosmic rays considered elsewhere), in which the large-scale field is generated by an imposed α-effect of variable intensity to explore the interplay between dynamo instability and MBI. The system evolves through three distinct phases: the linear (kinematic) dynamo stage, the onset of linear MBI when the magnetic field becomes sufficiently strong and the non-linear, statistically steady state. Non-linear effects associated with the MBI introduce oscillations which do not occur when the field is produced by the dynamo alone. The MBI initially accelerates the magnetic field amplification but the growth is quenched by the vertical motions produced by MBI. We construct a 1D model, which replicates all significant features of 3D simulations to confirm that magnetic buoyancy alone can quench the dynamo and is responsible for the magnetic field oscillations. Unlike similar results obtained with an imposed magnetic field, the non-linear interactions do not reduce the gas scale height, so the consequences of the magnetic buoyancy depend on how the magnetic field is maintained.

Publication metadata

Author(s): Qazi Y, Shukurov A, Tharakkal D, Gent FA, Bendre AB

Publication type: Article

Publication status: Published

Journal: Monthly Notices of the Royal Astronomical Society

Year: 2024

Volume: 527

Issue: 3

Pages: 7994-8005

Print publication date: 01/01/2024

Online publication date: 01/12/2023

Acceptance date: 27/11/2023

Date deposited: 04/01/2024

ISSN (print): 0035-8711

ISSN (electronic): 1365-2966

Publisher: Oxford University Press


DOI: 10.1093/mnras/stad3684


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Funder referenceFunder name
EU Horizon 2020
Ministry of Education and Culture Global Programme USA Pilot
Swedish Research Council (Vetenskapsrådet)